APETALA2 control of barley internode elongation.

V Patil,M Hansson,S M Mckim,J Morris,E Mollison,R Waugh,R Meikle,T Mcallister,H I Mcdermott,C Dockter,J C Silva,M Cummins,P E Hedley

doi:10.1242/dev.170373

Abstract

ABSTRACTMany plants dramatically elongate their stems during flowering, yet how this response is coordinated with the reproductive phase is unclear. We demonstrate that microRNA (miRNA) control of APETALA2 (AP2) is required for rapid, complete elongation of stem internodes in barley, especially of the final ‘peduncle’ internode directly underneath the inflorescence. Disrupted miR172 targeting of AP2 in the Zeo1.b barley mutant caused lower mitotic activity, delayed growth dynamics and premature lignification in the peduncle leading to fewer and shorter cells. Stage- and tissue-specific comparative transcriptomics between Zeo1.b and its parent cultivar showed reduced expression of proliferation-associated genes, ectopic expression of maturation-related genes and persistent, elevated expression of genes associated with jasmonate and stress responses. We further show that applying methyl jasmonate (MeJA) phenocopied the stem elongation of Zeo1.b, and that Zeo1.b itself was hypersensitive to inhibition by MeJA but less responsive to promotion by gibberellin. Taken together, we propose that miR172-mediated restriction of AP2 may modulate the jasmonate pathway to facilitate gibberellin-promoted stem growth during flowering.

Highlights

Plants undergo profound changes in architecture during postembryonic growth owing to altered activity within the shoot apical meristem (SAM) at the stem tip
Disrupted miR172-regulation of HvAP2 leads to fewer and shorter internode cells To determine whether Zeo1.b semi-dwarfism reflects fewer or shorter internodes or both, we examined each internode of the main stem or ‘culm’, numbered with respect to the peduncle (p) internode directly under the ‘spike’ inflorescence in Zeo1.b compared with Bowman (Fig. 1A)
Both leaves and internodes undergo a similar developmental programme of proliferation, expansion and maturation, leaf outgrowth occurs throughout vegetative development, whereas extensive internode growth only occurs after the reproductive transition

Summary

Introduction

Plants undergo profound changes in architecture during postembryonic growth owing to altered activity within the shoot apical meristem (SAM) at the stem tip. The SAM sequentially adds body parts to the vertical shoot axis, producing a stem of alternating leafy nodes and internodes (Bell and Bryan, 2008; Galinat, 1959; Gray, 1879; Sharman, 1942). Received 24 July 2018; Accepted 2 May 2019 and instead makes a flowering inflorescence, marking the start of the reproductive phase. Many plants respond to flowering by rapidly elongating existing vegetative internodes and new reproductive internodes, displacing the flowering tip upwards on a long stem (Bell and Bryan, 2008). Networks directing the SAM floral transition have received considerable attention (Wils and Kaufmann, 2017), how reproductive stem elongation is coordinated with flowering remains understudied (McKim, 2019)

Methods

Results

Conclusion